Dylann Roof, accused of killing nine African Americans in Charleston last year, indicted in state and federal courts.

The man accused of shooting nine African American churchgoers in South Carolina last year will face two death penalty trials, after federal prosecutors announced that they would seek capital punishment.

Dylann Roof, 22, allegedly joined an evening Bible study class at Emanuel African Methodist Episcopal Church in Charleston, then shot participants with a .45-calibre Glock handgun in June 2015. Three people survived the shooting.

He has been indicted for the killings in both state and federal court. It is not yet clear when the federal trial will begin.

"Following the department's rigorous review process to thoroughly consider all relevant factual and legal issues, I have determined that the Justice Department will seek the death penalty," US Attorney General Loretta Lynch said in a statement on Tuesday.

"The nature of the alleged crime and the resulting harm compelled this decision."

In a separate filing in US District Court in Charleston, federal prosecutors listed several aggravating factors that they said justified execution.

Roof "has expressed hatred and contempt towards African Americans, as well as other groups, and his animosity towards African Americans played a role in the murders," read the seven-page filing entered by Julius Richardson and Nathan Williams, assistant US attorneys.

The document also noted that Roof "demonstrated a lack of remorse" and "targeted men and women participating in a Bible study group at the Emanuel AME Church in order to magnify the societal impact".

Roof's defence attorneys did not immediately respond to requests for comment.

Racist views

Roof was arrested in North Carolina a day after the shooting.

A website attributed to him was later found to contain racist views towards African Americans, as well as photographs of Roof brandishing guns and the US South's historic Confederate battle flag.

In July, Roof pleaded not guilty to a 33-count indictment returned by a federal grand jury, including charges under a hate crime law that prohibits the use of force to harm an individual on the basis of race or colour.

He is also charged under a second hate crime law that bans the use of force to prohibit the free exercise of religious belief.

In addition, he stands accused of using a firearm to carry out what Lynch has called "racially motivated murders and attempted murders".

Roof's state trial, in which he is also facing murder charges, is set to begin on January 17, after a judge granted a delay requested by defence attorneys.

The local county prosecutor, Scarlett Wilson, said in September that she would seek the death penalty for Roof.

South Carolina Governor Nikki Haley has also backed execution in the case, describing Roof as "a person filled with hate".

Roof's attorneys have that said he would prefer to avoid execution by pleading guilty in exchange for life in prison.